The ever increasing traffic burden born by existing roadways has necessitated traffic regulating signal devices such as intelligent traffic control systems which are responsive to current traffic flow patterns. Historically such control systems involve embedded wires in the roadway such as described, for example, in U.S. Pat. No. 3,863,206 for "Digital Vehicle Detector". Such systems sense the passage of vehicles so that the signalling devices will give priority to the more heavily travelled roadways at intersections. Unfortunately such devices require wires spanning vehicle lanes. These spans of wire are subject to wear and if buried, the vibrations and shifting of the roadway caused by vehicle traffic and thermal expansion and therefor have a high failure rate. When a wire fails, the roadway must be dug up so that a replacement wire may be buried. Digging up the roadway may consist of simple narrow slit trenches a few inches wide but nevertheless the process interrupts traffic flow for hours or even days when complications arise. Furthermore, such devices only sense traffic waiting or crossing an intersection and therefore are useful only to cycle a traffic control device at intersections of infrequently traveled roadways with busy arteries whereby the traffic flow through the busy artery is not interrupted unless a vehicle is waiting in the less traveled roadway.
Prior attempts have been made to utilize vehicle sensing magnetometers to control traffic signalling devices such as the various systems developed by the Naval Surface Weapons Center of Silver Spring, Md. and described in their final report FHWA-RD-79-89 of October 1978 which is incorporated herein by reference. These devices proved successful in controlled experiments but failed to provide dependable service in an actual working environment. Therefore it is a primary objective of the present invention to provide a magnetometer means for sensing vehicular traffic combined with a computer control means for regulating traffic signalling devices which will operate reliably under the ambient conditions found in all traffic control situations.